The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to an active bolster mounted in a glove box door.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deployable air bag cushions that emerge from behind various openings upon inflation, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive. U.S. Pat. No. 8,474,868, issued Jul. 2, 2013, also incorporated herein by reference, discloses a typical structure wherein an active bolster includes an outer wall or trim panel that faces a vehicle occupant attached to an inner wall or panel along a sealed periphery. One or both of the walls is deformable in order to provide an inflatable bladder. For example, the inner bladder wall may have a pleated (i.e., accordion-like) region that straightens out during inflation.
The inner and outer walls of a typical active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They are typically injection molded but could also be blow molded. When formed separately, the walls must be hermetically joined around their periphery in order to form the inflatable bladder. The joint must be strong to resist separation as a result of the high pressures during inflation.
When incorporating an active bolster into the door for a glove box or other storage compartment, the inside back plate of the door (i.e., inner door liner) is required to act as a reaction surface or plate which must be relatively unmovable so that the inflating bladder and the front panel push outward, toward the vehicle occupant (instead of into the storage compartment). The inner door liner typically spans the opening so that the edges of the door overlap with the instrument panel or compartment frame in order to stop the door movement at a closed position.
It is desirable to fabricate the inner door liner from a moldable thermoplastic for low cost, low weight, and easy attachment to the bladder wall (e.g., by hot plate welding). One potential problem with such a construction is that it may have sufficient flexibility to bend during deployment of the bolster. Bending may in some instances cause a reduction of support for expansion of the bladder and a reduced ability to manage impact forces with the occupant. Bending needs to be limited in order to avoid submarining of the door through the door opening. The submarining can result in a partial loss of restraint force being applied toward the impacting body.
For aesthetic and functional reasons, the exterior side of the inner door liner should be smooth and without visible imperfections. For added strength to reduce bending, internally-projecting ribs have been integrally formed on the internal surface of the inner door liner when the liner is injection molded. However, the size of such rib features are limited by the injection molding process. Unless the ribs are kept relatively thin, the rib structure will “read through” to the exterior side of the liner because of differential cooling of the plastic. The ability to see the rib structure from the outside of the inner door liner may be perceived as a defect or a low quality product.